Viscous fan coupling DIY repair

How the device works

It was invented in the USA in 1917 by engineer Melvin Severn. This product did not immediately find its application, so it was not recognized for a long time. In 1964, a viscous coupling was installed in the Interceptor FF, where it acted as an automatic differential lock. Only in 1965 did this mechanism take its place in the engine.

A viscous coupling is a device that is responsible for rotating a special fan that cools the system thanks to a special liquid. It looks like a round mechanism made of a silicone base and filled with a lubricant. The viscous coupling ensures smooth fan control.

There are flat disks inside the product body. Some of them are connected to the drive shaft, while others are connected to the driven shaft. There are various protrusions and holes on their surface. Design features place these elements in close proximity to each other. The silicone liquid located inside tends to thicken with strong stirring. It also expands when heated, so it creates a lot of pressure on the disks when the engine is running and compresses them together.

Features of the mechanism

At first glance, the operating principle of a viscous cooling fan coupling seems complicated, but it is not. The movable crankshaft is driven into rotation and transfers its energy to the clutch. This makes its silicone base softer and more viscous. The clutch begins to block, causing the second disk with the fan to rotate.

Almost every engine has a viscous coupling. This is due to the importance of its functions and the quality of the device, because it is at a fairly high level. The viscous coupling has an excellent safety mechanism: when a person, through his own negligence, puts his hand into the moving element, he will stop to prevent injury.

Checking the cooling fan

It is not always possible to use the car regularly, so it ends up in a state of downtime. At this time, the viscous coupling requires checking its performance. This will also help prevent damage from wear and tear.

Recognizing a malfunction is not easy under normal conditions, but there are methods for checking the viscous coupling of a fan. To inspect the mechanism, you need to check the speed of the product with the engine turned on, warm and cold. When the engine is cooled, there should be no extraneous sounds, and the speed should be normal. A hot engine can often provoke various noises and irregularities in the speed.

Such problems can arise due to faulty bearings or untimely oil changes. Also, sealed seals and leakage of silicone fluid can cause failure.

Solving the problem yourself

If defects in operation are found, the viscous coupling does not always have to be replaced. These problems can often be solved on your own. One of the most common problems encountered with this device is silicone fluid leakage. To make up for the deficiency, you need to do the following:

1. Disassemble the viscous coupling by removing it from the water pump.
2. It's worth taking a closer look at the product's disk. On its surface there is a special plate with a spring, under which there is a hole for silicone. It is necessary to remove the pin with extreme caution and pour lubricant inside using a special syringe. During this process, the part itself must be placed in a horizontal position.
3. It will be enough to pour 15 milliliters of liquid into the syringe.
4. You need to wait a few minutes until the substance flows into the viscous coupling without removing the syringe.
5. After checking that the procedure was performed correctly and that there is no excess silicone, the part can be installed back.

For those who do not consider themselves experienced motorists, it is better not to engage in such work, because this can cause complete breakdown of the device. Typically, the biggest challenge is putting everything back together.

Other problems

Bearings can often cause failure of a viscous coupling. This is evidenced by the appearance of unusual noises in the cooling zone. But you can also repair it yourself:

1. To repair the product, it must be removed from the main motor structure. To do this, unscrew the 3 bolts on which the bearings are attached.
2. These elements should be replaced only after the oil fluid has been drained and the unit has been disassembled. To simplify the process, you can use a special tool - a puller. You should not use improvised devices, as they can permanently damage the parts.
3. After installing the bearing, you can install the entire device into the motor mechanisms. Before this, you need to fill in fresh silicone, which was drained before replacing parts.

Basic malfunctions of Viscous coupling

It is immediately worth noting that manufacturers of cars equipped with viscous couplings indicate in the technical documentation that this unit cannot be repaired, and in case of interruptions in its operation, it must be replaced with a new one.

There are two main malfunctions that may occur during the operation of a VM:

• The seal of the product body is broken, resulting in silicone oil leaking out of it. In this case, the viscous coupling simply stops working and does not “turn on” the temporary all-wheel drive mode or block the differential.
• Hardening of the silicone liquid and, as a result, loss of its “unique” properties (this can happen due to frequent overheating of the unit, for example, during constant off-road driving). This type of malfunction results in both shafts being in constant engagement. But transmission elements (drive axle gearbox, gearbox, etc.) of cars with temporarily connected all-wheel drive are not initially designed for such constant increased loads and can quickly fail. Therefore, at the first sign that the liquid has “turned” into a solid state, the viscous coupling must be urgently replaced. Inaction can lead to very expensive repairs.

Features of repair work

As some motorists may have noticed, the viscous coupling does not always have a hole for filling silicone fluid. In this case, you can do it yourself, but beginners should not do this so as not to damage the product. It is better to turn to craftsmen who will do careful drilling.

Repair of the viscous fan coupling should be carried out without brute force. The main material of the device is aluminum, which can simply be bent and completely destroy the viscous coupling.

The operation of a car depends on many mechanisms that must work as a whole. If even one element fails, the serviceability of the entire vehicle is disrupted. The viscous coupling is necessary for the normal operation of the cooling fan. The safety of the trip depends on this, so you need to monitor its performance.

Repairs to the viscous cooling fan coupling should only be carried out by specialists. Of course, you can do this yourself, but any mistake can damage the device. You need to take care of service work in advance.

The design of a car's cooling system contains such an interesting mechanism as a viscous coupling. Questions related to this mechanism are often asked on automobile forums. We concluded that a detailed study of this topic is necessary.

Pro tip: a faulty viscous coupling cannot be repaired

Almost all modern cars are equipped with non-removable viscous couplings, which are completely impossible to repair, especially in a home garage. But there are still several models, mostly made in Germany, whose design allows you to replace bearings and silicone fluid.

When a viscous coupling bearing fails, this can be determined by a characteristic howl from under the hood. If there is a leak of silicone liquid from the housing, the efficiency of the coupling is significantly reduced - the fan begins to rotate more slowly, and may even stop completely. The same “symptoms” can be observed when disks fail.

So, if your car has a dismountable model, you can try to repair it yourself:

First you need to remove the fan. As a rule, it is enough to unscrew 3 and 4 bolts. By removing the fan, you can more accurately assess the condition of the viscous coupling. If the bearing is damaged, then before removing it it is necessary to drain all the silicone liquid through a hole specially designed for this purpose. After this, use a screwdriver to carefully pry out the plate that covers the bearing itself. Next, use a puller to remove the bearing and install a new one. The bearing is pressed into the seat using a special mandrel. In this case, it is strictly forbidden to hit the bearing race with a hammer or inflict any blows at all.

If there is not enough fluid inside the viscous coupling, this can be determined quite easily by the sudden stop of the fan after the engine is turned off. In addition, the engine begins to overheat due to a drop in fan speed. Silicone liquid is added to the coupling using a special syringe. However, you can also use an ordinary medical one, the largest “caliber” that can be found.

As for damage to the disks, it can only be accurately determined by completely disassembling the viscous coupling. Disks cannot be repaired.

It is not difficult to completely replace the viscous coupling of a cooling fan. The unit that has become unusable is removed from the engine and the impeller is unscrewed. Install a new part. When installing, make sure that the bolts are tightened sufficiently tightly. Next, the fan is installed in its place. It should be noted that in the vast majority of cases it is much easier and faster to change a viscous coupling than to bother with its repair and restoration.

What is a viscous fan coupling?

This strange name refers to a special mechanism that has a selective transmission function, determined by external conditions and torque. The coupling has the appearance of a sealed housing. Inside it are disks divided into two rows. One row of disks is connected to the driven shaft, respectively, the second row is connected to the drive shaft. The design of the mechanism provides for the possibility of alternating disks among themselves. Their design has holes and protrusions.

Inside the viscous coupling there is a special liquid with a viscous structure, which is why the mechanism is often called viscous. Most often, silicone is used to make this substance. The liquid is characterized by unique features that determine its effective use. The capabilities of this substance are as follows:

• with increasing stirring intensity, the viscosity index increases;
• When heated, the expansion coefficient increases.

Such features determine the operating principle of the viscous coupling, which will be studied further.

Viscous cooling fan coupling

Where is the viscous coupling located?

This mechanism takes place between the car’s radiator and the pump pulley. It performs a number of important functions:

1. Controlling the speed of rotation of the fan blades, which cools the vehicle's power unit.
2. Ensuring engine efficiency by activating the fan at the right moments.
3. Reducing the load experienced by the power unit.

The coupling can be mounted on a flanged shaft, which, in turn, is mounted on a pump pulley. The shaft can also be screwed onto the pump shaft. Next you need to understand how the viscous coupling of the cooling fan works.

How does a viscous cooling fan coupling work?

Getting to know the viscous fan coupling will be impossible without studying the operating principle of this mechanism. To an inexperienced motorist, this process may seem complicated, although, in fact, everything is simple and clear. The operating principle of the viscous cooling fan coupling is based on the functioning of a bimetallic sensor. It is located in front of the viscose fan. This element reacts to the temperature transmitted through the radiator of the cooling system.

Scania R-Series

1. At low temperatures, a sensitive sensor causes the valve to contract. This results in the oil inside the viscous coupling being retained within the reservoir. The clutch on the fan is deactivated and continues to rotate at only 20% of the motor rotation intensity.
2. When the temperature rises to the operating level, the sensor expands and causes the valve to rotate. This causes the oil to move around the chamber to the outer edges. The fan clutch is activated and the clutch rotation speed increases from 20% to 80%.

When the vehicle moves at a constant speed, the rotation of the disks is uniform and is not accompanied by mixing of oil between them. When a difference occurs between the rotation speeds of the shafts (driven and driven), the disks also begin to operate in different modes. This leads to an increase in the viscosity of the silicone fluid. In this state, it affects the transmission of torque.

If there is a large difference between the rotation speeds of the disks, the liquid becomes almost solid, which leads to blocking of the viscous coupling. We have studied the design of the viscous fan coupling; now we need to learn how to check the proper operation of this mechanism.

What can a faulty viscous coupling cause?

When replacing the pump, it is always recommended to check the condition of the viscous fan clutch. A damaged coupling will directly affect the life of the pump. A faulty viscous fan clutch may remain stuck in the engaged position, meaning it will always run at 80% of engine speed. This can cause a breakdown with high levels of noise and vibration, creating a loud swirling sound as engine speed increases and fuel consumption increases.

On the other hand, if the viscous fan connection fails in the off position, it will not move air through the heatsink. This, in turn, will cause the engine to overheat when the cooling process stops.

How to check a viscous coupling

The performance of the viscous fan coupling must be checked on a cold and hot power unit. This is evidenced by operational manuals for vehicle repairs. When the engine is cold, re-gassing will not change the clutch rotation speed. In the case of a hot engine, this figure will increase significantly.

It is also necessary to check the longitudinal play; if it is detected, work will have to be done to eliminate it. The presence of extraneous sounds during clutch rotation will indicate a bearing malfunction.

Main causes of malfunction

The mechanism can fail for several reasons. We have identified the main and most common:

• the use of tires of different sizes, which also have different levels of wear;
• fluid leakage from the coupling;
• wear of parts as a result of intensive use, exposure to aggressive factors and high temperatures;
• incorrect alignment of the drive mechanism;
• loss of properties of the bimetallic sensor, which can occur as a result of surface oxidation and jamming of the coupling;
• faulty bearing condition.

Types of viscous couplings

On the automotive spare parts market you can find two main types of viscous couplings:

1. The first type is characterized by a constant volume of dilatant fluid.
2. The second type has a different volume of silicone, which changes depending on external influences.

The first type of viscous coupling is used for limited slip differentials in transmissions, including automatic all-wheel drive systems. They are used in internal cooling systems.

If the part operates in normal mode with average loads, and the car moves on a high-quality road surface, the angular velocities of the two axes remain the same.

The rotation of the clutch discs is almost uniform, and torque is transmitted from the engine to the driven axle with minimal load. As a result, the vehicle can operate in both all-wheel drive and rear-wheel drive.

But if the car gets into rough terrain or drives on ice and mud, the uniformity of rotation is seriously reduced, and the viscosity of the silicone increases significantly. This increases the transmission of torque to the second axle. In some cases, the power transfer rate reaches 100 percent.

At the same time, the viscous coupling cannot replace a full-fledged differential, which redistributes the torque of the power plant to both axles. It is advisable to use this design on uneven surfaces and rough terrain.

It will also be justified when driving:

• on ice;
• city ​​streets;
• wet track.

If driving is carried out completely off-road, the clutch should engage instantly. otherwise, the torque transmission system will fail, resulting in the need for expensive and complex repairs.

In most modern cars with automatic transmissions, viscous couplings operate in the so-called “pre-start mode”. It is characterized by a uniform transfer of 5-15% of the motor power to the driven axle, which negatively affects the reaction time of the unit.

Main causes of malfunction

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If you carry out timely routine maintenance of the viscous coupling, its service life is at least 200,000 kilometers. Considering that most of the cars on which such drives are installed have a significant mileage, the owners of these cars have encountered problems with viscous couplings more than once.

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The main causes of the malfunction include:

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• natural wear and tear;
• changing the parameters of bimetallic plates;
• bearing wear;
• fan impeller beating (partial destruction of the impeller);
• gel leakage, untimely filling, change in gel structure;
• mechanical damage.

Also, premature failure of work may be accompanied by clogging of the radiator cell blowing area and contamination of the design of the coupling itself.

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Symptoms of a problem

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The main sign of a viscous coupling malfunction is engine overheating . This happens mainly if the gel has leaked out, or the bimetallic plate does not work in time. In this case, when the engine temperature rises, the fan does not start to rotate or rotates at low speeds, not providing normal cooling of the radiator.

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A reverse malfunction, when the fan begins to rotate on a cold engine, often occurs when the physical parameters of the gel change, numerous viscous coupling components fail, or the lubricant hardens.

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Viscous cooling radiator coupling, how it works, where it is installed

The operation of the viscous coupling of the cooling radiator directly depends on its design, thanks to which the fan does not operate constantly, but depending on the temperature of the coolant. Thanks to this, the cooling system works as efficiently as possible. The cooling radiator vicoupler consists of a solid oval-shaped body. There are two disks inside the case. One disk is rigidly attached to the cooling fan impeller shaft. The other is mounted directly on the shaft, which is connected to the engine drive. The discs “float” in a special silicone liquid. The viscous coupling design also includes a special bimetallic plate.

The whole system works as follows:

If the air temperature is normal, then both disks are either at a minimum distance from each other or slightly mesh. However, in any case, the disks slip relative to each other. This means that in this case the fan does not work. As the temperature rises, the bimetallic platinum begins to shrink and bend, squeezing the silicone liquid out of the reservoir. The pressure on one of the disks begins to gradually increase, the disks begin to press against each other - the fan begins to rotate. When the temperature drops, the bimetallic strip gradually returns to its original position, the pressure inside the coupling drops, the discs separate and the fan stops.

The radiator viscous coupling is installed on the pump shaft together with the fan. Sometimes the structure is mounted on the crankshaft - it all depends on the specific car model. It should be noted that a fan with a viscous coupling is a much more efficient system than a conventional impeller mounted on a shaft. The viscous coupling operates as needed, without cooling the engine unnecessarily, for example, in winter. Most often, a fan with a clutch is installed on cars designed for heavy loads:

• Trucks. • Crossovers. • SUVs. • Sports cars, etc.

Advantages and disadvantages

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A malfunction of the cooling system is a critical malfunction of the car, in which further independent movement is impossible. Therefore, the main consumer characteristic of a viscous coupling is reliability. From this position, it is higher than in the case of an electric radiator fan.

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Many car owners are familiar with the problem when, after the winter season, they have to repair the electric drives of the radiator fans and the electronic control circuit of the engine cooling system. There are no electrics or electronics in the viscous coupling system, which is a big plus.

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Another advantage of a viscous coupling is the greater power it can provide to the fan shaft. Theoretically, this power can be equal to the entire shaft power of the internal combustion engine, that is, several kilowatts. Electric motors for radiator fans of passenger cars have a power of about several tens of watts. Therefore, the use of viscous couplings has not yet been abandoned in powerful agricultural, construction, and military equipment.

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• the complexity of the technical design, the difficulty of repair, it is easier and cheaper to replace it as a unit (entirely);
• has a large mass, exerts a mechanical load on the shaft;
• control of its switching temperature is not sufficiently accurate;
• increased noise at high engine speeds;
• when carrying out routine maintenance, it is necessary to fill (refill) the viscous coupling with gel or oil of a certain viscosity; such technical characteristics are difficult to find in reference books;
• additional engine power take-off.

These and other shortcomings have practically replaced viscous couplings from cooling systems of internal combustion engines of passenger cars.

Restoring the engine cooling system

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If the viscous coupling fails, the first step is to refill it with oil or gel. There are no exact recommendations on this matter; usually you have to experiment.

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You can try to find specialized specialists, but it’s easier and cheaper to find a used one at a disassembly site. If the search for a working viscous coupling is unsuccessful, you can think about replacing the cooling system with a conventional one with an electric drive.

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Video - replacing a viscous coupling with an electric fan on a BMW:

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You can install an electric cooling system using a simplified scenario. To do this you will need the following components:

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• an electric cooling fan that can be adapted to your radiator;
• a set of wires with a cross-section of at least 6 sq. mm;
• 40 Amp fuse;
• automotive relay for a current of at least 30 Amperes;
• thermal relay, maybe a Zhiguli one with an operating temperature of 87 degrees Celsius.

The thermostat can be installed on a radiator or on a metal surface near the thermostat by gluing. Next, you need to assemble an electrical circuit for turning on the fan similar to the VAZ one. Such a simple scheme can last for five seasons without failure.

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Viscous coupling repair on Pajero: bearing replacement

1. There are no fundamental differences in removing the device. You need to remove three bolts holding the impeller in place, and then three more to remove the cover.
2. Next, after removing the viscous coupling, carefully remove the upper disk, which serves to block the fan.
3. The entire device is lubricated with special oil. Repair the viscous coupling so as to preserve it. If you don’t know the exact name of the liquid, it will be extremely difficult to find it.
4. Simply replacing the bearing will not work, since you first need to grind off the flare on the shaft.
5. Place the device in a vice for greater ease of repair.
6. The bearing also needs to be ground down. If this is not done, the base of the viscous coupling may be seriously damaged.
7. Buy a sealed bearing with no visible balls at any automotive store. Its cost is no more than 100 rubles.
8. Before seating the bearing, lubricate the seat with sealant.
9. Assemble the viscous coupling and then install it in the car.

Recommendations

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Constantly check the timing of the viscous coupling, especially in the warm season, and monitor the engine temperature in traffic jams. If it approaches critical values, seriously think about replacing the viscous coupling with an electrical system. By the way, these two systems can operate in parallel for greater reliability.

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Video - replacing the viscous cooling fan coupling on a Toyota Mark 2:

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